Glossary for system administrators
Envelope
An envelope refers to the communications between the sending and receiving systems up to the transmission of the email itself. This includes the system handshake and the exchange of the sending and receiving addresses. These details do not need to match the details in the email itself. Envelope information is typically entered in the email header.
DKIM
DKIM (or DomainKeys) is an identification model for emails. A digital signature is used when creating the email. A public key is required to decrypt the message. If decryption of the digital signature works, it can be assumed that the email sender is not spoofed.
Opt-in
Opt-in refers to a process by which the consumer explicitly agrees to be contacted for advertising purposes.
Reverse DNS entry (FQDN)
A Reverse DNS entry or FQDN (Fully Qualified Domain Name) is the unique name of an internet host. The FQDN can be used to discover the host's IP address. The Reverse DNS entry should be used as the HELO when sending emails.
SPF (Sender Policy Framwork)
SPF (Sender Policy Framework) is a technology designed to make it more difficult to spoof sender addresses. It ascertains the IP addresses from which emails with a specific sender domain can be sent (or from which IP addresses mails may not be sent). To allow this to happen a TXT type (or SPF type if it exists) resource record is created in the DNS zone; it lists all the authorised IP addresses used as sending addresses in the domain.
To check your SPF entry, we recommend the SPF Wizard
on the Openspf.org site.
SRS (Sender Rewriting Scheme)
When an email is redirected, a receiving system that validates email reception against an SPF entry is unable to validate the sender's identity. Forwarding servers should use SRS to encapsulate the sending address in an envelope to prevent SPF validation returning incorrect results.
For more information on SRS refer to the Openspf.org site.
